The actions described in this cluster of projects aim to capture CO2 from industrial fumes and ambient air, convert it to e-fuel de-fossilised fuels and use it in combustion units. This project focuses on the use of e-fuels in decentralised energy systems for combined heat and power generation, also known as cogeneration. In addition to the use in large conventional power plants, we argue that it is necessary to have more diffuse production such as renewable energy. In this project, we focus more specifically on piston engines. These are currently widely used with traditional fuels in decentralized systems due to their better electrical performance. However, the transition to the combustion of e-fuels still poses some challenges, particularly with regard to the combustion of ammonia. The specific objectives of the CRUCIAL_COGENEF project are: study the use of a co-product of the production of e-fuels, i.e. oxygen (either from electrolysis during the production of hydrogen or from the separation of nitrogen from air for the production of ammonia). This oxygen is usually released into the atmosphere, which represents a loss. It could be used in engines to facilitate CO2 capture. Two types of engines are envisaged in the project: traditional positive-ignition engines and low-temperature combustion engines (HCCI). The latter, in the form of homogeneous charge compression ignition (HCCI), begins to come out of laboratories and find commercial applications. For both modes, many challenges remain. The positive ignition engine, although it is the reference for gaseous fuels, still presents difficulties related to the production of pollutants and could see its efficiency evolve. The HCCI engine poses challenges in terms of control.